There are several processes known in the art for the production of ultra high purity oxygen; among these are U.S. Pat. Nos. 3,363,427; 4,560,397 and 4,615,716.
U.S. Pat. No. 3,363,427 discloses a process and an apparatus for the purification of a commercially pure oxygen feedstock by cryogenic distillation. The process basically liquefies the oxygen feedstock and rectifies the liquified oxygen in a single distillation column operating at a pressure slightly above atmospheric and a vapor-to-liquid ratio in excess of 0.700.
U.S. Pat. No. 4,560,397 is a process for the production of ultra high purity oxygen and elevated pressure nitrogen by cryogenic rectification of air wherein the product oxygen is recovered from a secondary column at a point above the liquid sump while impurities are removed from the column at a distance from the product withdrawal point.
U.S. Pat. No. 4,615,716 discloses a method of oxygen recycle on the bottom section of the low pressure column of a dual pressure column system. This along with an increase in the bottom section reboil vapor rate allows an appreciable increase in the production rate of ultra high purity oxygen and a substantial decrease in power required as compared to conventional processes.